This is the oddest thing, and I've never seen in before. When someone tries to call add me to a call (making it a 3 way conference call), I'm either muted, or they can't connect at all. Anyone else seem to have this issue?
Yes I have the same issue, I was also getting dropped calls with Wifi calling enabled so I disabled that. I am on MetroPCS in the US and I think there is a bug tracker for this on the Google issues board.